Fisheye lenses with a field angle, that is, an entire picture angle, of nearly one hundred eighty degrees are known. These fisheye lenses, which may be used in video imaging devices, form images on a single picture surface, which may be circular in shape, with high distortion aberration so that areas as well as the borders of the image are distorted, along with increasing the field of view and the need for image processing. Furthermore, using computer software, modern techniques for removing distortion aberration that appears in images encourages greater use of fisheye lenses.
On the other hand, the high resolution obtainable in newer imaging devices, accompanied by computers with faster processing, make further advances in high performance of fisheye lenses desirable. In addition, there is also strong demand for high portability of these imaging devices, along with a demand for compactness of the fisheye lens of the imaging device.
Japanese Patent No. 3396839 describes fisheye lenses with a relatively small number of lens elements and that provide a field angle, that is, an entire picture angle, of about one hundred eighty degrees. Additionally, Japanese Laid-Open Patent Application S53-083623 describes similar fisheye lenses.
The fisheye lenses described in Japanese Patent No. 3396839 use an equal solid angle projection and the fisheye lenses described in Japanese Laid-Open Patent Application S53-083623 use equidistance projections. However, neither of these publications describes fisheye lenses with satisfactory off-axis performance. In particular, all the aberrations in the fisheye lenses described in Japanese Laid-Open Patent Application S53-083623 are large, and none of these lenses meet the current requirements for achieving high performance.